Methanol plant retrofit for acetic acid manufacture

Abstract

The retrofitting of an existing methanol or methanol/ammonia plant to make acetic acid is disclosed. The existing plant has a reformer to which natural gas or another hydrocarbon and steam (water) are fed. Syngas is formed in the reformer. All or part of the syngas is processed to separate out carbon dioxide, carbon monoxide and hydrogen, and the separated carbon dioxide is fed either to the existing methanol synthesis loop for methanol synthesis, or back into the feed to the reformer to enhance carbon monoxide formation in the syngas. Any remaining syngas not fed to the carbon dioxide separator can be converted to methanol in the existing methanol synthesis loop along with carbon dioxide from the separator and/or imported carbon dioxide, and hydrogen from the separator. The separated carbon monoxide is then reacted with the methanol to produce acetic acid or an acetic acid precursor by a conventional process. Also disclosed is the reaction of separated hydrogen with nitrogen, in a conventional manner, to produce ammonia. Also disclosed is the reaction of a portion of the acetic acid in a conventional manner with oxygen and ethylene to form vinyl acetate monomer. The nitrogen for the added ammonia capacity in a retrofit of an original methanol plant comprising an ammonia synthesis loop, and the oxygen for the vinyl acetate monomer process, are obtained from a new air separation unit.

What is claimed is:  
     
       1. A method for manufacturing a product from carbon monoxide and methanol selected from the group consisting of acetic acid, acetic anhydride, methyl formate, methyl acetate and combinations thereof, comprising the steps of: 
       operating at least one steam reformer to convert a hydrocarbon to a syngas stream containing hydrogen, carbon monoxide, and carbon dioxide;  
       separating all or part of the syngas stream into respective streams rich in carbon dioxide, carbon monoxide and hydrogen;  
       operating a methanol synthesis loop to convert a feed comprising (1) carbon dioxide and (2) a portion of the hydrogen-rich stream, to methanol;  
       reacting at least a portion of the carbon monoxide-rich stream from the separation unit with the methanol from the methanol synthesis loop in essentially stoichiometric proportions to form the product.  
     
     
       2. The method of claim  1  wherein the feed to the methanol synthesis loop comprises imported carbon dioxide. 
     
     
       3. The method of claim  2  wherein the feed to the methanol synthesis loop includes a portion of the synthesis gas. 
     
     
       4. The method of claim  2  wherein essentially all of the syngas stream is supplied to the separation step. 
     
     
       5. The method of claim  1  wherein the amount of the hydrogen-rich stream is in excess of the stoichiometric hydrogen required by the methanol synthesis loop. 
     
     
       6. The method of claim  1  wherein essentially all of the carbon dioxide-rich stream is supplied to the synthesis loop. 
     
     
       7. The method of claim  1  wherein essentially all of the carbon monoxide-rich stream is supplied to the reaction step. 
     
     
       8. The method of claim  1  wherein the reaction step comprises the intermediate formation of methyl formate and isomerization of the methyl formate to acetic acid. 
     
     
       9. The method of claim  1  wherein the reaction step comprises the intermediate reaction of CO and two moles of methyl alcohol to form methyl acetate and hydrolysis of the methyl acetate to acetic acid and methanol. 
     
     
       10. A method for manufacturing a product from carbon monoxide and methanol selected from the group consisting of acetic acid, acetic anhydride, methyl formate, methyl acetate and combinations thereof, comprising the steps of: 
       operating at least one steam reformer to convert a hydrocarbon to a syngas stream containing hydrogen, carbon monoxide, and carbon dioxide;  
       supplying a major portion of the syngas stream to a separation unit for separating the syngas stream into respective streams rich in carbon dioxide, carbon monoxide and hydrogen;  
       operating a methanol synthesis loop with a feed comprising the carbon-dioxide-rich stream from the separation unit, a minor portion of the syngas stream, and an additional source of carbon dioxide to produce a methanol stream;  
       reacting the carbon monoxide-rich stream from the separation unit with the methanol stream from the methanol synthesis loop in essentially stoichiometric proportions to form the product.  
     
     
       11. The method of claim  10  wherein the reaction step comprises the intermediate formation of methyl formate and isomerization of the methyl formate to acetic acid. 
     
     
       12. The method of claim  10  wherein the reaction step comprises the intermediate reaction of CO and two moles of methyl alcohol to form methyl acetate and hydrolysis of the methyl acetate to acetic acid and methanol. 
     
     
       13. A method for manufacturing a product from carbon monoxide and methanol selected from the group consisting of acetic acid, acetic anhydride, methyl formate, methyl acetate and combinations thereof, comprising the steps of: 
       operating at least one steam reformer to convert a hydrocarbon to a syngas stream containing hydrogen, carbon monoxide, and carbon dioxide;  
       supplying the syngas stream to a separation unit for separating the syngas stream into respective streams rich in carbon dioxide, carbon monoxide and hydrogen;  
       operating a methanol synthesis loop with a feed comprising the carbon-dioxide-rich stream from the separation unit, a portion of the hydrogen-rich stream from the separation unit, a minor portion of the syngas stream, and carbon dioxide from an additional source, to produce a methanol stream;  
       reacting the carbon monoxide-rich stream from the separation unit with the methanol stream from the methanol synthesis loop in essentially stoichiometric proportions to form the product.  
     
     
       14. The method of claim  13  wherein the reaction step comprises the intermediate formation of methyl formate and isomerization of the methyl formate to acetic acid. 
     
     
       15. The method of claim  13  wherein the reaction step comprises the intermediate reaction of CO and two moles of methyl alcohol to form methyl acetate and hydrolysis of the methyl acetate to acetic acid and methanol. 
     
     
       16. A process for making hydrogen and a product selected from the group consisting of acetic acid, acetic anhydride, methyl formate, methyl acetate and combinations thereof, from a hydrocarbon via intermediate methanol, carbon monoxide, and carbon dioxide, comprising the steps of: 
       reforming the hydrocarbon with steam to form a syngas containing hydrogen, carbon monoxide, and carbon dioxide;  
       recovering heat from the syngas to form a cooled syngas stream;  
       compressing the cooled syngas stream to a separation pressure;  
       processing the syngas in a separation unit to separate a carbon monoxide-rich stream from the hydrogen and carbon dioxide;  
       operating a methanol synthesis loop to react a first portion of the hydrogen from the separation unit with the carbon dioxide from the separation unit and additional carbon dioxide from another source to obtain a methanol stream;  
       reacting the carbon monoxide-rich stream from the separation unit with the methanol stream from the methanol synthesis loop in essentially stoichiometric proportions to form a product selected from the group consisting of acetic acid, acetic anhydride, methyl formate, methyl acetate and combinations thereof.